The House and the Senate have a split personality by design, but Wednesday's debut of the 112th Congress revealed a stark contrast between the two chambers that could define the direction of every major debate over the next two years.

At one end of the Capitol, a House brimming with fresh faces and ambitious goals was sworn into office, its exuberant new Republican leaders pledging to derail President Obama's agenda and dramatically scale back the size of the federal government.

At the other end, a more somber Senate convened, its Democratic majority intact - albeit much smaller after the November elections. Whereas many of the House freshmen are new to politics, the 13 senators in the class of 2010 are a more seasoned lot. Their first order of business: a debate of filibuster rules.

The two lawmakers sworn in to lead the House and Senate are archetypes of the moment. Rep. John A. Boehner (R-Ohio), the son of a bar owner, rode the tea party wave to one of the biggest midterm election victories in recent history and is eager to deliver by repealing health-care reform and making deep cuts to federal programs. Immediately after Boehner, 61, accepted the speaker's gavel from Nancy Pelosi (D-Calif.), now the minority leader, the House began debating changes to budget rules that would force spending reductions.

"Hard work and tough decisions will be required of the 112th Congress," Boehner said in his acceptance speech. "No longer can we fall short. No longer can we kick the can down the road. The people voted to end business as usual, and today we begin to carry out their instructions."

The new Senate leader is the old Senate leader, Harry M. Reid (D-Nev.), the son of a miner, who narrowly won a fifth term in November against a tea party opponent. As he opened the new Senate, Reid, 70, pleaded for his Republican colleagues to end what he called their obstructionist ways, setting the tone for coming battles over deficit reduction, the war in Afghanistan, health-care reform and taxes.

"The most important change we can make in the 112th Congress is to work better and more closely as teammates, not as opponents - as partners, not as partisans - to fulfill our constitutional responsibility to pursue a more perfect union," Reid said.

The day's crescendo came shortly past 2 p.m., after the formal roll-call vote for the gavel concluded with Boehner receiving 241 votes and Pelosi 173, ending her historic four-year reign as the nation's first female House speaker.

Pelosi - whose fate has been sealed since Nov. 2, when Democrats lost 63 seats and the majority - held two grandchildren on her lap as the House clerk called the name of every member. She waved to Democrats who symbolically supported her continued tenure despite concerns about whether she's the right face for the party.

Pelosi strode to the speaker's chair for a final speech, congratulating Boehner but also proclaiming victory in pushing a progressive agenda. "I now pass this gavel and the sacred trust that goes with it to the new speaker. God bless you, Speaker Boehner," she said to cheers from the chamber.

Despite the confidence of the new House leaders, few of the items on their agenda are likely to end up in law as conceived - beginning with the GOP effort to repeal Obama's health-care law, set for a final vote next Wednesday. Reid has vowed to block the effort in the Senate. But Senate Democrats face a similar problem with their priorities, including immigration reform, which many of the House GOP freshmen oppose.

A secondary plotline for the 112th Congress will be the potential divide within party ranks, as both Boehner and Reid face ambitious backbenchers trying to shake up the systems that the two leaders have come to master.